Group services such as Push-To-Talk (PTT) services, wherein one device can communicate simultaneously with other designated communication devices in a group, have been in use for years, such as in two-way trunked-radio dispatch systems for example. A typical dispatch two-way radio communication system comprises communication units, communication resources, communication sites, and a communication resource allocator. Each of the sites has a substantially distinct coverage area and is geographically located throughout the system. Each site also has a number of communication resources assigned to it, where at least one of the communication resources is used as a control channel, while a number of the remaining communication resources are used as voice channels. Such systems are known to use frequency division multiple access (FDMA) and time division multiple access (TDMA) methods to rebroadcast transmissions, for example.
In a system that supports dispatch group calls, the communication units are typically arranged into communication groups (talkgroups) and may be located anywhere within the system (in any site). When a communication unit of a talkgroup requests a group call, it transmits, via a control channel of the site in which it is located, an inbound signaling message to the communication resource allocator. (A group call typically allows all members of the same talkgroup that are located within the system to communicate with each other.) The inbound signaling message generally comprises the requesting communication unit's individual identification number, the requesting communication unit's talkgroup, and a request for a group call. Upon receiving the inbound signaling message, the communication resource allocator will allocate a dedicated voice channel in any necessary sites to the requesting communication unit's talkgroup.
Thus, in dispatch systems a dedicated forward link is established (one in each site where communication units are present) and monitored by all units involved in the group call in that site, and a single reverse link which is used by the group member who is currently transmitting to the other members. Non-transmitting talk group members are typically in a listen only mode (i.e., not able to transmit when another member is talking) and thus are not allocated a dedicated reverse link.
More recently, in response to an ever-accelerating worldwide demand for mobile and personal portable communications, code division multiple access (CDMA) have proven to be a popular system for serving large populations of multiple access users over analog or other digital technologies, such as for the Third Generation Partnership Project (3GPP) for example. CDMA is well suited for cellular communications, but is only know being employed in a system supporting group services, such as PTT. However, implementing PTT service in different types of communication networks, such as CDMA, have inherent problems that must be solved if groups services are to enjoy widespread and efficient use.
Currently, group services such as PTT and Push-to-Video, or more generally Push-to-Something (PTx) services are provided by a network in multiple cells based on the IP protocol stack. However, two disadvantages have been observed: a) a larger setup delay is introduced, which is intolerable for Push service, and b) there is as inefficient utilization of the air interface. Group service is characterized by one-to-one or one-to-many communication. For PTT services over WCDMA as currently implemented each communication device or user equipment (UE) participating in a group session is in dedicated channel (Cell_DCH) state. Each UE in addition to the “talker ” is receiving data from the single source on a dedicated channel, and is transmitting dedicated control channel in the uplink for synchronization and inner loop power control. In cells where there are many UEs participating in the same group session, the remaining throughput of the cell is reduced considerably due to the radio resources (code and power) assigned to multiple copies of the data from the single source on the downlink and also due to the associated uplink dedicated control channels.
A Multimedia Broadcast Multicast Service (MBMS) has been introduced to broadcast information simultaneously to multiple users. However, MBMS cannot be used for group call services in a one-to-many communication as is required for PTx services
What is needed is a system and method to alleviate the aforementioned problems.